Any material, whether natural or synthetic, must exhibit satisfactory resistance to degradation under conditions of use, if products made from the materials are to find a lasting market. A lack of satisfactory resistance to degradation usually manifests itself as a partial or total loss of structural integrity, a darkening or discoloration of the product, a loss of flexibility or resilience, or a combination of the above phenomena. These phenomena are promoted or catalyzed by air (oxygen), heat and light, particularly ultraviolet light.
To protect materials, ingredients which can be collectively called stabilizers are admixed with the materials to prevent or inhibit degradation. These stabilizers work in diverse and complex ways, such that a compound which stabilizes against heat and oxygen degradation in a material may not stabilize against light degradation in the same material, or vice versa. Furthermore, a compound which acts as a stabilizer against oxygen degradation in one type of material may be relatively inactive in another type of material. Thus compounds which are stabilizers are further classed as antioxidants, antiozonants, heat stabilizers and ultraviolet (UV) light stabilizers, depending upon what type of activity and stabilization they demonstrate. In many cases, to obtain optimum protection, a mixture of compounds, each specifically selected to afford maximum protection against a certain type of degradation, is often used. In some instances stabilizers are deliberately chosen to counter the adverse effects of a plasticizer which, though highly effective as a plasticizer, tends to accelerate UV degradation. In other words, the plasticized material is more susceptible to degradation than if no plasticizer was added. As a general empirical rule, it is found that plasticizers are marginally effective as stabilizers, and stabilizers are marginally effective as plasticizers, it being more likely that a compound with desirable stabilizer properties has undesirable plasticizer properties, and vice versa.
The present invention is directed to (a) novel UV light stabilizers classed as hindered amines more specifically classed as hindered cyclic diazaalkanes, and (b) novel compositions in which the cyclic diazacycloalkanes are incorporated. The basic structure of these novel compounds is a polysubstituted 1,5-diazacycloalkane having (a) a fixed three-carbon bridge between the two N atoms (the N.sup.1 and N.sup.5 atoms) of the diaza ring, the remaining portion of the ring having a variable length bridge of two or more carbon atoms, and (b) at least the N.sup.5 -adjacent carbon atom of the fixed three-carbon bridge has two substituents (hence "polysubstituted"), which may be cyclizable, that is, form a cyclic substituent. These compounds which may be monocyclic, or with cyclizable substituents, may be bicyclic or tricyclic, are particularly useful as UV light stabilizers in substantially colorless organic compounds, and particularly in polymeric substrates. They may also form dimers and bis-compounds. The diaza ring of the basic structure may have from 6 to 9 ring members, more preferably from 6 to 8 ring members, and most preferably from 6 to 7 ring members.
It is known that 2-keto-4,4,6,6-tetramethyl-1,5-diazacycloheptane may be prepared by a Schmidt's rearrangement of a six-membered ring with sodium azide (see German Pat. No. 2,428,877) but there is no known manner of similarly arriving at an eight membered, 1,5-diaza ring with an N.sup.1 -adjacent carbonyl. Moreover, though the foregoing 2-keto-diazacycloheptane, identified as 2,2,7,7-tetramethyl-5-oxo-1,4-diazacyclopheptan in the reference, can be synthesized as described, other polysubstituted compounds named cannot be so synthesized. More specifically the 2-keto-1,5-diazapolycycloalkanes named therein cannot be synthesized as described. The foregoing lactams which may be made as described in this German patent, and many other lactams which may be made as described in U.S. Pat. Ser. No. 835,069, may be reduced, for example, with lithium aluminum hydride, to form the 1,5-diazacycloalkanes which are found, like the lactams, to be excellent UV light stabilizers.
It is known that 1,5-benzodiazepin-2-spirocycloalkanes may be made in a one-step condensation from o-phenylenediamine and cyclic ketones such as cyclohexanone in cold ethanol in the presence of boron trifluoride-ether complex. ("Synthesis of Hetrocyclic Compounds. Part XX1X. Substituted 2,3-dihydro-1H-1,5-benzodiazepines" by Herbert, John A. A. and Suschitzky, Hans, J. C. S. Perkin I, 1974, 2657.) However, 1,2-diaminocyclohexane does not react under similar conditions. The lactams of this reference may also be reduced with a metal hydride to yield the 1,5-diazacycloalkanes used in the composition of this invention.
Further, it is known that .alpha.,.beta.-unsaturated ketones may be added slowly to a methanol solution of an aliphatic 1,2-diamine at about 30.degree. C., and the mixture hydrogenated over an Adams catalyst to give 7-alkyl-1,5-diazacycloheptanes also identified as 2-alkyl-1,4-diazacycloheptanes (Bonvincini A. and Cantatore G., Chem. Ind. 54,980 (1972); New Methods in Synthetic Organic Chemistry Selected from the Current Chemical Literature, August 1974). There is no disclosure which might suggest the use of the substituted alkanes as UV light stabilizers in organic polymers.
It is also known that cyclo condensation of .beta.,.beta.-dimethylacrylic acid with o-phenylenediamine and its derivatives yields 2-keto-1,5-benzodiazepines (Khakimova, N. K. et al, Inst.Khim.Rast.Veshechestv, Tashkent, USSR: USB.Khim.Zh.1975, 19(2), P 53-55). The N.sup.5 -adjacent carbon of the fixed three-carbon ring is disubstituted, and the benzene ring may have a hydrogen, chlorine or methyl substituent. The reference compounds have no utility as UV light stabilizers. It has now been found that, under strenuous hydrogenating conditions of above about 200.degree. C. and 2000 psi, the 2-keto-1,5-benzodiazepines of the Russian reference may be hydrogenated in alcohol to the 2-keto-decahydro-benzodiazepine without rupturing the ring structure, though we are aware of no teaching that would indicate a seven-membered, 1,5-diaza ring could withstand such strenuous conditions, or that such hydrogenation could be accomplished. Though the lactams are excellent stabilizers, it has been found that the alkanes, produced by reducing the lactams, are also excellent UV stabilizers.
In fact, known quinioline derivatives such as 1,2,3,4-tetrahydro-3,3,6 (or 7)-trimethylquinoline is not hydrogenated under similar conditions, namely 200.degree. C. and 2000 psi in the presence of Raney's nickel, but decomposes.
Except for the 2-keto-1,5-diazacycloheptane compounds disclosed in the aforementioned German reference there is no teaching to suggest that polysubstituted 1,5-diazacycloalkanes and polycyclic polysubstituted 2-keto-1,5-diazacycloalkanes would be effective UV-light stabilizers.